Method of solid state bonding an article to a tube surface

ABSTRACT

An article of manufacture consisting of a fastener bonded to an exposed surface of a tube by a solid state pulse resistance weld at the faying interface between the fastener and the tube to form an integral unitary structure. The method of producing the unitary structure involves the utilization of unique welding structures wherein the parts being integrated are disposed in juxtaposed position followed by a time phased application of a force pulse and an electrical energy pulse to the assembled parts to produce a solid state resistance weld at the faying interface to achieve the desired structure.

United States Patent Anderson [is] 3,666,910 [451 May 30, 1972 [54]METHOD OF SOLID STATE BONDING AN ARTICLE TO A TUBE SURFACE 21 Appl. No.2112,250

521 U.S.Cl ..219/107,2l9/86,2l9/9l,

' 219/117,219 119 s1 lnt.Cl ..B23k 11 04 [58] FieldofSearch..219/85,ll7,9l,78,86,1l9

[ 56] References Cited UNITED STATES PATENTS 2,305,042 12/1942 Thacker..2l9/9l 8/1969 Helms et al. ..2l9/86 x 5/1969 Gwynn etal. ..2l9/ll7RPrimary Examiner-J. V. Truhe Assistant Examiner-L. A. SchutzmanAttorneyWilson & Fraser [5 7] ABSTRACT An article of manufactureconsisting of a fastener bonded to an exposed surface of a tube by asolid state pulse resistance weld at the faying interface between thefastener and the tube to form an integral unitary structure. The methodof producing the unitary structure involves the utilization of uniquewelding structures wherein the parts being integrated are disposed injuxtaposed position followed by a time phased application of a forcepulse and an electrical energy pulse to the assembled parts to produce asolid state resistance weld at the faying interface to achieve thedesired structure.

7 Claims, 4 Drawing figures 40 PULSE WELD WELD POWER WELDING l2 r HTRANSFORMER SWITCH POWER SUPPLY 11:"- \IB I CONTROL l6 UNIT 24 I 22 Mg 34o K38 FORCE FORCE POWER FORCE MECHANISM MECHANlSM SWITCH POWER SUPPLYPatented May 30, 1972 2 Sheets-Sheet 2 N Q h- INVENTOR. DAV I D G.ANDERSON ZJ NLM- Jomkzou 6 vm NM ATTORNEYS METHOD OF SOLID STATE BONDINGAN ARTICLE TO A TUBE SURFACE BACKGROUND OF THE INVENTION lnassemblieswhere it is desired to affix a threaded fastener, for example, to theexterior wall of a thin wall metal tube, the objective can be achievedonly with considerable difficulty and expense. Typically, brazingtechniques are employed to effectively produce the ultimate article. Insuch joining techniques, a fluxing material is needed to clean the metalsurfaces of the parts to be joined. Also, a metal filler material isrequired and the parts must be heated to a temperature above the meltingpoint of the metal filler. The melted metal filler then spreads out overthe flux cleaned metal areas to effectively wet the facing surfaces ofthe parts to be joined.

Elaborate fixture mechanisms or joint preparation is necessary in thebrazing techniques that are employed in order to assure that thefastener is precisely located on the tube. These locating means mustremain in position at least until the assembly of parts has cooledsufficiently for the molten metal filler material to solidify.

Another type of welding which has been considered for bonding a fastenerto a tube is conventional resistance projection welding. However, it hasbeen found that said welding technique resultsin damage to the tube andtherefore is unacceptable. The heat required to effect the desired weldbyprojection welding is of such a magnitude that distortion and severemetal expulsion occur. Also, the inside surface of the tube is damagedby the burning through" during projection welding.

Electron beam welding has also been considered for the above purpose,but electron beam welding requires the electron beam to be confined to avery narrow region to cause localized melting of the tube and theassociated fastener. To achieve the desired and necessary bond between afastener and a tube, the electron beam must be moved at a controlledrate and along a discrete path to produce a weld of sufficient strength.Among the other disadvantages of electron beam welding include the highcost of the required equipment; the complexity of maintenance and repairproblems due primarily to the associated high voltage and high vacuumsystems; and the melting of the parts being bonded which is necessary toproduce the weld requires somuch heat energy that undesired distortionof the parts may occur.

SUMMARY The disadvantages of the presently known techniques forachieving the objectives are substantially overcome by the utilizationof the method and apparatus of the present invention resulting in a newarticle of manufacture. The objectives and advantages of the inventionare achieved by disposing the parts to be integrated in contactingrelationship followed by a time phased application of force pulse and anelectrical energy pulse to the assembled parts to establish a currentdensity within the range of from 500,000 to 3,000,000 amperes per squareinch of weld interface for a period of typically the order of 0.5 to 5.5milliseconds to effectively weld the parts together to form an integralunitary article.

BRIEF DESCRIPTION OF THE DRAWINGS Other objectives and advantages of theinvention will become readily apparent to those skilled in the art fromreading thefollowing detailed description of an embodiment of theinvention when considered in the light of the accompanying drawings inwhich:

FIG. 1 is a flow diagram of the method of the invention;

FIG. 2 is a schematic diagram of one typical form of the electrodestructure and associated system FIG. 3 is a fragmentary sectional viewof the electrode structure illustrated in FIG. 2 taken along line 3-3thereof; and

FIG. 4 is a perspective view of the completed unitary structure formedby the apparatus illustrated in FIGS. 2 and 3.

DESCRIPTION OF PREFERRED EMBODIMENTS As diagrammatically illustrated inFIG. 1, the invention is concerned with a process for bonding two partsof electrically conductive metal together to form a unitary integralarticle. More specifically, the invention relates to a process forproducing a solid state pulse resistance bond or weld between a thinwalled tube and a fastener of electrically conductive metal to form aresultant unitary article of manufacture. The process involves the timephased application of a force pulse and a pulse of electrical energy ofa current density within the range of from 500,000 to 3,000,000 amperesof the weld or faying interface of the parts being joined.

To completely understand the process of the invention, as illustrated inFIG. 1, reference will be made to the bonding of a fastener 10 to theouter surface of a tube 12 as specifically illustrated in FIGS. 2 and 3.At the commencement of the process, and with particular reference toFIGS. 2 and 3, the two parts 10 and 12 of electrically conductive metalsuch as, for example, mild steel (1010) wherein the tube 12 has athickness of 0.058 inches are disposed in a manner wherein there iscontact between a surface of the head 11 of the fastener 10 and theouter surface of the tube 12. An upper electrode 14 is provided with aninternal cavity for containing the shank portion of the fastener 10. Alower electrode 16 is provided to support the tube 12. The uppermostelectrode 14 is mounted on an upper platen or fixed support 18electrically insulated therefrom by a layer of insulating material 20.The lowermost electrode 16 is mounted for unitary movement on a lowerplaten 22 and is electrically insulated therefrom by a layer ofinsulating material 24. The lower platen 22 is coupled to forcemechanism 30 which may provide for selective reciprocating movement ofthe electrode 16 relative to the electrode 14 to initially enable thedisposition of the parts 10 and 12 therebetween. At such stage in theoperation, the electrodes 14 and 16 are moved toward one another untilthe assemblage of the parts 10 and 12 are in contacting relation.

The force mechanism 30, which typically includes a pressure transducer,is efiective to apply a force pulse on the lower platen 22, which issuperimposed on the initial forces applied by the initial closingmovement of the electrodes 14 and 16 by the relative closing movement ofthe associated platens 18 and 22. The specific mechanism employed fordeveloping the force by the force mechanism 30 may be of the typeillustrated and described in the U.S. Patent to AC. Vang U.S. Pat. No.3,059,094 issued Oct. 16, 1962. It will be understood that in a timephased relation with the application of a force pulse on the sheets 10and 12 by the force mechanism 30, an electrical energy pulse is appliedto the electrodes 14 and 16, as will be explained in greater detailhereinafter.

It has been found that in practice, pressures developed of the order offrom 2,000 to 3,000 pounds have been employed to produce satisfactorysolid state welds with the described process. These pressures are notconsidered to be critical and may be varied over a rather wide range.The pressures imposed on the system can be imposed in sinusoidal waveform, and, typically, the force pulse is initiated first and before theforce pulse reaches the maximum amplitude, the electrical energy pulseis commenced. Typically, the electrical energy pulse is then allowed tofully decay before the full decay of the force pulse. The electricalenergy pulse is developed in the system illustrated in FIG. 2 in thesecondary winding of a pulse weld transformer 32 which has its primarywinding coupled, to a weld power supply 34 through a suitable weld powerswitch 36. The weld power supply 34 typicallyincludes a bank ofcapacitors and a charging circuit which are effective to produce aninstantaneous source of electrical energy to the pulse weld transformer32 as will be explained in greater detail hereinafter.

The force mechanism 30 is coupled to a force mechanism power supply 38through a force power switch 40.

The weld power switch 36 and the force power switch 40 are controlled intimed relation to one another by a process control unit 42. The controlunit 42 is effective to energize the respective power switches 36 and 40in such a fashion that, typically, the force power switch 40 isenergized to commence the application of force by the lower platen 22 toapply a force pulse at the interface of the parts and 12. Then, thecontrol unit 42 is effective to energize the weld power switch 36 toallow the capacitors of the weld power supply 34 to discharge andproduce an electrical energy pulse in the primary winding of the pulseweld transformer 32. The secondary winding of the pulse weld transformer32 causes a high electrical energy pulse between the electrodes 14 and16 and the parts 10 and 12. An electrical energy pulse having a currentdensity of the order of from 500,000 to 3,000,000 arnperes per squareinch of weld interface has been satisfactory for achieving the desiredresults of the invention of obtaining a solid state bond. In operationof the illustrated embodiment, the force pulse peaks in the order offrom 0.5 to 2.0 milliseconds before the electrical energy peaks.

It has been theorized that the phenomenon involved in the weldingprocess of the invention involves electrical energy at the interface ofthe parts 10 and 12 in magnitude sufficient to establish atomic bondsacross the interface, resulting in a solid state pulse resistance weld.The electrical energy pulse applied by the pulse transformer 32 followsan electrical path through the electrode 14, the parts 10 and 12, andthe electrode 16.

The control unit 42 is typically energized after the lower platen 22 andthe upper platen 18 are initially closed to a point where the sheets 10and 12 are firmly held between terminal ends of the electrodes 14 and16. The energized control unit 42 initially signals the force switch 40to couple the force mechanism 30 to its power supply 38 to effectivelyimpart a force pulse of 8.0 millisecond duration, for example, with apeak force of approximately 2,000 pounds to the platen 22, causing thesheets 10 and 12 to be bonded to be forced tightly against the adjacentoverlapped surfaces.

Typically, the control unit 42 is programmed to energize the weld powerswitch 36 coupling the pulse transformer 32 to the welding power supply38 to thereby apply an electrical energy pulse to the electrode elements14 and 16. The energization thereof commences, in the describedembodiment, prior to the instant the force pulse reaches its peakamplitude.

The lower electrode illustrated in FIGS. 2 and 3 is comprised of a mainbeam portion 16 having an upper supporting surface which is contoured toconform generally to the shape of the internal surface of the tubularmember which it is to support. The beam portion 16 of the lowerelectrode is supported by a pair of horizontally spaced supports 16'which in turn are supported on a base support 16". The supports 16' arespaced apart horizontally a sufficient amount so that the tubular member12 can be accommodated therebetween. At the conclusion of a weldingcycle the beam portion 16 of the lower electrode is removed from thesupports 16' to permit the removal of the tubular member 12 and the thenintegral fastener 10.

It will be understood that while it has been described that the lowerplaten 22 is movable satisfactory clearance could likewise be achievedby providing movement of the upper platen 18.

The invention has produced a novel method of producing a compositestructure formed of a fastener 10 and a thin walled tube 12 wherein theparts are formed of a heat modifiable material and the total energynecessary to effect the bond or weld therebetween is minimal. Aperspective view of the unitary article is illustrated in FIG. 4.

above described invention produces a unitary structure formed of atleast a pair of cooperating overlapped parts of electrically conductivematerial wherein, in each instance, the weld is formed in the zonedefined by the overlapped portion of the parts. Thereby, the electricalpath through the parts being welded is well defined and contributes tothe minimization of heat energy buildup in the weld zone to effectivelyprevent any crystalline deformation of the internal structure of themetal being welded. The novel unitary structure of the invention and themethod of forming the structures is of a substantial consequence to thefield of welding and enables the production of parts heretoforeimpossible to achieve.

In accordance with the provisions of the patent statutes, I haveexplained the principal mode of operation of my invention and haveillustrated and described what I now consider to represent its bestembodiments. However, I desire to have it understood that the inventionmay be practiced otherwise than as specifically illustrated anddescribed without departing from its spirit or scope.

What I claim is:

1. A method of welding a part of electrically conducting material to atube of electrically conductive material comprising:

providing a first surface of said part;

providing a second surface of said tube;

engaging said first and second surfaces;

providing a pair of opposed cooperating electrodes, one of saidelectrodes engaging said part and the other of said electrodes contouredto contact an extended portion of the inner surface of said tube;

imposing a force pulse on the faying interface between said first andsecond surfaces to urge said surfaces into intimate contact; and

applying an electrical energy pulse between said electrodes to produce acurrent density within the range of from 500,000 to 3,000,000 per squareinch of faying interface between said first and said second surfacesdesired to be welded in time phased relation with said force pulse toproduce a solid state resistance bond to weld said surfaces together toform an integral bonded article.

2. The method as defined in claim 1 wherein said electrical energy pulseis applied as a single pulse.

3. The method as defined in claim 2 wherein said electrical energy pulseis of a duration of from 0.5 to 5.5 milliseconds.

4. The method defined in claim 1 wherein the force pulse applied to saidsurfaces arrives at its peak amplitude before the electrical energypulse arrives at its peak magnitude.

5. The method as defined in claim 1 wherein said part is a fastener.

6. The method as defined in claim 5 wherein said fastener includes athreaded shank portion and an integral head portion, said head portioncontaining said first surface.

7. The method as defined in claim 5 wherein the wall of said tube is ofthe order of 0.05 inch in thickness.

1. A method of welding a part of electrically conducting material to atube of electrically conductive material comprising: providing a firstsurface of said part; providing a second surface of said tube; engagingsaid first and second surfaces; providing a pair of opposed cooperatingelectrodes, one of said electrodes engaging said part and the other ofsaid electrodes contoured to contact an extended portion of the innersurface of said tube; imposing a force pulse on the faying interfacebetween said first and second surfaces to urge said surfaces intointimate contact; and applying an electrical energy pulse between saidelectrodes to produce a current density within the range of from 500,000to 3,000,000 per square inch of faying interface between said first andsaid second surfaces desired to be welded in time phased relation withsaid force pulse to produce a solid state resistance bond to weld saidsurfaces together to form an integral bonded article.
 2. The method asdefined in claim 1 wherein said electrical energy pulse is applied as asingle pulse.
 3. The method as defined in claim 2 wherein saidelectrical energy pulse is of a duration oF from 0.5 to 5.5milliseconds.
 4. The method defined in claim 1 wherein the force pulseapplied to said surfaces arrives at its peak amplitude before theelectrical energy pulse arrives at its peak magnitude.
 5. The method asdefined in claim 1 wherein said part is a fastener.
 6. The method asdefined in claim 5 wherein said fastener includes a threaded shankportion and an integral head portion, said head portion containing saidfirst surface.
 7. The method as defined in claim 5 wherein the wall ofsaid tube is of the order of 0.05 inch in thickness.